This invention relates generally to the field of gas chromatographs and, more specifically, to a portable low-power gas chromatograph.
Gas chromatography has long been used as an analytical technique for the identification and quantification of individual chemical compounds within a sample. A gas chromatograph is an analytical instrument that separates a gaseous sample (or a sample that has been converted to a gaseous state) into its constituent components. A typical gas chromatograph includes an injector that converts samples to a gaseous state (if needed) and moves the gaseous sample to the head of an analytical column in a narrow band; an analytical column, typically a long, coiled tube or the like, that separates the sample into its constituent components; a detector that detects and measures the constituent components as they emerge from the analytical column; and a data display for displaying the results of the analysis to a user. The constituent components of the sample are separated in the analytical column due to differential interactions between the components and an immobilized liquid or solid material within the column.
A typical gas chromatograph is heavy and not easily transported for use in the field. Light-weight, portable gas chromatographs are needed for a number of reasons. One such need is for support of required chemical analysis under the Chemical Weapons Convention (CWC). Under the CWC, there must be onsite analysis of samples during a three-day challenge inspection of a location. Sample analysis using the approved CWC gas chromatograph/mass spectrometer can take 45 to 90 minutes, thereby limiting the number of samples that can be analyzed. An instrument capable of quickly screening collected samples would greatly reduce sample analysis backlog under the CWC.
In addition, personnel conducting inspections for the CWC must enter various military and commercial facilities where highly dangerous chemicals may be present. A portable gas chromatography system provides the ability to maximize worker safety by sampling and analyzing the air at a location within a matter of minutes. A gas chromatography system that is capable of operating from a battery pack, has a self-contained gas supply, and is easily portable by one person could be used for such onsite monitoring.
Since the events of Sep. 11, 2001, the need for a portable, lightweight gas chromatograph capable of selectively detecting low and mid-levels of chemical warfare agents is a high priority. Such a device is needed to fill the gap between the gross-level hand-held detectors and the fixed-site continuous monitors used at military installations. Such a device could, among other things, be used to define the boundaries of a chemical incident, monitor the direction, speed and dissipation of a poison gas, monitor entry into an unknown area or environment, and provide near real-time monitoring and alarm at the scene of an incident.
A number of instruments potentially competitive with the low-power gas chromatograph of the present invention are currently available or under development in commercial and military markets. Each of these devices, however, has some limitation that is overcome by the present device. The available systems are divided into three categories and are discussed below.
Fixed Installation Instruments. This category is dominated by the Automatic Continuous Air Monitoring System (ACAMS), produce by ABB Process Analytics, and the MINICAMS, produced by CMS Research (U.S. Pat. Nos. 4,805,441 and 5,014,541). Both instruments are similar in operation and system design and both use a solid adsorbent collection media and a GC column wrapped around an aluminum mandrel for heating. The MINICAMS has multiple detector modules, including a pulsed-flame photometric detector, that can be exchanged to allow for detection of various compounds.
These instruments are not designed to be mobile air monitors, although both have been used as such after installing them onto trucks or vans. Instead, they were designed to continuously monitor a fixed location and sound an alarm if chemical agents are detected. Neither instrument has an onboard gas or power supply, both require AC line current and are extremely heavy.
Gross or High Level Instruments. Many gross level detectors are commercially available and supplied by several manufacturers. Most of these instruments use ion mobility spectrometry (IMS) as a detection mechanism and are capable of detecting chemical agents in the low ppm or high ppb concentration ranges. These instruments are handheld and battery powered. They required 0.5 to 2 minutes for chemical agent detection and provide a yes/no type answer as to the presence of an agent at concentrations where immediate health risks exist. They are not sufficiently sensitive to indicate whether a concentration of chemical agent exists at levels where mid or long-term exposure presents a health risk.
MINI GC. There are several portable GC systems that are currently available or in the prototype phase of development. Manufacturers include SRI International, Agilent, Analytical Specialist Inc., and RVM Scientific, Inc. Analytical Specialist, Inc., for example, is marketing the Microfast GC (U.S. Pat. No. 5,611,846). This device uses column technology that is similar to that used in the low-power gas chromatograph of the present invention. The Analytical Specialist device, however, uses a thermal conductivity detector, which does not provide sufficient sensitivity or selectivity for purposes of the present invention.
RVM Scientific has developed a beta portable GC (U.S. Pat. No. 6,223,584) that does use a pulsed flame photometric detector and analytical GC column, however the device currently lacks the ruggedness required to make it acceptable for a wide range of field uses. The device also has limited utility as a laboratory instrument for analysis of injectable samples and lacks the capacity to provide continuous air monitoring. The patent also discloses a significant limitation with the design in that the GC system has a leak rate of 0.1 mL/min.
Other gas chromatographs produced by Agilent and SRI are designed for laboratory operation and are not capable of air sampling without modification or addition of second party equipment being added.
The low-power gas chromatograph of the present invention addresses these and other concerns as outlined below.